There are a range of clinical syndromes that require some form of ventilation therapy. These syndromes may include hypoxemia, various forms of respiratory insufficiency, and airway disorders. There are also non-respiratory and non-airway diseases that require ventilation therapy, such as congestive heart failure and neuromuscular disease, respectively. Typically, patients receiving gas through these ventilation therapy systems require the addition of humidification to the gas being delivered to prevent the gas from drying the airways. Additionally, it is also known that with oxygen therapy, if oxygen is delivered for an extended time at flow rates greater than 6 lpm, the airways will dry, and artificial humidification is required.
In existing systems, humidification is added by passing the delivered gas through the vapor phase of a humidifier or bubbling the gas through water. For mechanical ventilators, the gas delivery tubing, or patient circuit, that fluidly transmits the breathing gas from the ventilator to the patient in existing systems is sized to provide for low pressure drop between the ventilator and the patient. This tubing is sized at 15 mm or 22 mm inside diameter. To prevent the vapor from condensing within the tubing, an adjunctive technique of heating the gas delivery tubing or thermally insulating it with protective sheathing is commonly applied.
A new generation of mechanical ventilators is emerging that utilizes smaller tubing to transport the breathing gas to patients. The gas delivery tubing of this new generation of ventilators is in the range of 2-14 mm inside diameter, compared to 15 mm or 22 mm inside diameter for currently available systems. Correspondingly, the pressures achieved within the new gas delivery tubing can be 0-80 psig higher than ambient pressure, whereas the pressure inside of tubing from currently available ventilators is typically within 1 psig of ambient pressure. Due to the smaller diameter and higher pressure of the gas delivery circuit of newer mechanical ventilator systems, there is a corresponding need for new humidification systems.
Addtionally, some of the new generations of mechanical ventilators utilize an open airway technology, wherein the air passage between the ventilator and the patient is not sealed, as it is in traditional mechanical ventilator systems. The systems utilizing open airway technology provide for ambient air to be entrained near the patient interface via a venturi system in addition to the gas delivered from the ventilator, wherein the gas delivered to the patient is the combination of the gas delivered from the ventilator plus the entrained air. With the newer open systems, it may be challenging and inefficient to add humidification to the delivered gas using conventional methods. Therefore, a need exists for new humidification technologies compatible with the open airway technology.
Furthermore, the new generations of mechanical ventilators are designed to emphasize use during walking and mobility, whereas existing ventilation systems tend to limit mobility to applications such as when patients are confined to a wheelchair. Existing humidification systems typically use water tubs that are large and orientation sensitive, and are typically heated by systems that consume more power than is practical to power by a portable battery source. For these reasons, existing systems are typically only used to provide humidification when the patient is stationary. Therefore, an additional need exists for humidification technologies that are small, lightweight and portable.
Existing humidification systems typically do not have precise control of the amount of water introduced into the system, and they are not synchronized with the patient's breathing patterns. Typically, existing systems can provide humidification levels above 90% relative humidity, even though some studies have shown that patients typically cannot perceive a benefit for humidification levels above 50% relative humidity. Additionally, because existing systems either have continuous intentional leaks or exhalation flows, and because patients nominally exhale twice as long as they inspire, existing humidification systems can consume up to three times the water that is required if the systems only provided water during the patient's inspiratory cycle. Additionally, by providing more humidification than is required by the patient's needs, existing humidification systems often have problems with excessive “rainout” or condensation in the tubing, leading to the requirement of water traps in the tubing to catch excess water to prevent adverse effects due to patients and equipment aspirating water that collects in the system. Additionally, when used during sleep, some patients complain of the existing humidification systems soaking their pillows with water because of the excess humidity provided. For these and other reasons, an additional need exists for humidification systems that can precisely control the amount of humidification added and/or to synchronize the humidification with the patients' breathing patterns.
Because existing systems typically heat water to vaporize it, they can experience performance degradations that are caused by solids that are left behind by other water sources containing dissolved solids, such as tap water, and for this reason, they typically require the use of distilled water with their systems. However, users of humidification systems would prefer not to have to deal with the expense and inconvenience of acquiring distilled water for their systems. Therefore, an additional need exists for humidification systems that do not require distilled or other specialized water.